Performance Evaluation of Base Course Gravel and Fine Subgrade Combinations for In Situ Cementitious Stabilisation of Pavements

In situ stabilisation of existing pavement materials is a valuable rehabilitation treatment for secondary and local roads that are generally comprised of a gravel base course with a thin bituminous surface. However, sometimes the required stabilisation depth exceeds the existing base course thickness, meaning some portion of the underlying subgrade is incorporated into the stabilised material. The aim of this research was to determine the effect of subgrade inclusion on the unconfined compression strength (UCS) of the stabilisation material, as an indicator of the performance of stabilised base course and subgrade blends. It was found that three different subgrades, each at 20%–50% of the total granular material, achieved acceptable UCS values with 3%–7% of a triple-blend cementitious binder. Furthermore, it was found that pre-mixing of the hydrated lime component into the granular material was more beneficial when reactive clay subgrades were encountered. In the future, in situ cementitious stabilisation of combined base and subgrade materials (referred to as ‘basegrade stabilisation’) should not be resisted, as long as the associated UCS values are generally in the acceptable range of 1–2 MPa.